The present invention relates to an image forming apparatus comprising an image recording unit for electrostatistically transferring a toner image formed on the surface of an image carrier (a photosensitive substance) to paper which is carried, while being drawn in, by a belt-like or a drum-like paper carrier, and a paper feeding unit which feeds the paper to the image recording unit. More particularly, the present invention relates to an image forming apparatus designed to facilitate correction of paper jams.
In a conventional image forming apparatus, paper drawn in by a paper carrier is sometimes drawn against an image carrier at an image transfer position of the paper carrier. In such a case, the paper drawn by the image carrier is drawn into a cleaner unit disposed along the surface of the image carrier downstream with respect to the image transfer position, thereby causing a paper jam (a paper-on-photoreceptor jam which will be hereinafter referred to as a POP jam). To facilitate the correction of such a paper jam, a technique as disclosed in the Unexamined Japanese Patent Application Publication. No. Hei. 1-109383 is already known. This patent publication discloses a technique which rotates a transfer drum in a reverse direction when a paper jam is detected by paper jam detecting means disposed in a separating pawl unit.
However, according to this technique, if a part of the paper still remains upstream with respect to transfer rolls (in many cases, a resi-roll is used for the transfer rolls) of the main unit of the image forming apparatus when the POP jam arises, that part of the paper remains sandwiched between the resi-rolls even when the transfer drum is rotated in a reverse direction. If a drawer unit (a removable member) is removed from the main unit of the image forming apparatus together with the paper carrier while the part of the paper sandwiched between the resi-rollers, the paper becomes torn. A small piece of the paper thus remains between the resi-rolls, which makes it difficult to remove the remaining piece of paper.
Further, according to the previously mentioned technique, if the POP jam occurs which trailing end of the paper has passed an inlet chute, the rotation of the paper carrier in a reverse direction in this state causes the trailing end of the paper to burrow its way under the inlet chute. If the drawer unit including the paper carrier is removed from the main unit of the image forming apparatus, the trailing end of the paper is caught by the main unit of the image forming apparatus outside the drawer unit. In this case, the trailing end of the paper has an appearance as if it has been trimmed with a guillotine. Eventually, a small piece of paper remains in the main unit of the image forming apparatus, which makes it difficult to remove the remaining piece of paper.
For these reasons, it is difficult to reliably remove jamming paper from the image forming apparatus with the conventional technique only by means of a simple operation such as the removal of a detechable unit from the apparatus.
If a POP jam arises while paper is stretched between the paper carrier and the resi-rollers, if the paper is conveyed into the inlet chute by letting the trailing end of the paper pass through the resi-rollers, the paper will become concertinaed within the inlet chute. To make it possible to contain such concertinaed paper in the inlet chute, an interval between an upper paper guide and a lower paper guide of the inlet chute should be previously set to a sufficiently large size, or should be made variable. In either case, the height of the concertinaed paper within the inlet chute becomes increased.
When the removable drawer unit is removed from the main unit of the image forming apparatus in order to correct the paper jam, an attempt to rake the concertinaed paper out of the inlet chute results in the paper being caught by a fixed member, such as a frame, of the main unit of the image forming apparatus. As a result, the paper becomes torn. It is not easy to remove a small piece of paper thus remaining in the main unit of the image forming apparatus.
In a system which rotates the image carrier and the paper carrier in a reverse direction when the POP jam occurs, the following problems are encountered if a cleaner of the paper carrier is provided with a wiper blade.
Specifically, as a result of rotation of the paper holder in a reverse direction, the leading edge of the wiper blade that is in contact with the paper carrier curls up. If the leading edge of the wiper blade is left in the curled up state for a long period of time, the wiper blade becomes deformed or is deteriorated. As a consequence, the cleaning capability of the image forming apparatus deteriorates very quickly. For this reason, it is desirable to correct the curled up leading edge of the wiper blade in a shorter period of time.
If the POP jam was not detected, or was detected late, the paper is pulled into the cleaner unit of the image carrier, which makes it difficult to correct the POP jam. According to a known conventional method of detecting the POP jam, a paper sensor detects paper coiled around the image carrier. However, this method has such a problem that the circumferential length of the image carrier becomes longer because the paper sensor occupies a part of the space around the image carrier.
For this reason, with regard to an image forming apparatus in which a toner image having a plurality of colors is transferred onto paper, it is proposed that a light reflecting paper sensor is not disposed around the image carrier but along the surface of a belt or drum-like paper carrier.
The light reflecting paper sensor is arranged so as to detect light reflected from white paper, and hence the sensor receives light reflected from an image on one side of the paper when both faces of the paper are copied. If a dark image is formed on one side of the paper, it becomes impossible to detect the paper.